Any idea what it could be? Shop couldn’t find anything wrong.

 

perhaps a bad A/C relay! I've moved your post into the right area in the RDX section

 

how easy is that to change?

 

The relay for the A/C is in the underhood fuse box, right below the brake fluid reservoir. The labeling is inside the cover.
That said, it may be that the system is shutting down as a failsafe. If anything gets out of spec, the system will shut down to protect itself.
Might be fine once it sits.
You might just have to have the system charge checked. Maybe the operation of the compressor clutch or the radiator fans. There are a lot of things to check.

Define "shop" You need to be at the dealer (a Honda dealer would do) or an A/C specialist.

 

1. Look to see if you have any B codes for the climate control system.
2. Hook up R134 gauges and check operation of system
3. Check freon charge with a full drain and fill using recovery system. A low charge will cause evaporator to freeze and clog with ice
4. Check your expansion valve for proper operation.
5. Check pressure switch and temp switch.